It’s Earth Day, though you could be forgiven if you missed it. The annual event doesn’t quite have the same energy as it once did — especially not compared with the first Earth Day 43 years ago. That nationwide event, initially inspired by the work of Wisconsin Senator Gaylord Nelson, was celebrated by more than 20 million people in more than 12,000 events around the country. As Nicholas Lemann pointed out in a recent piece in the New Yorker, Congress took the day off, and two-thirds of its members — Democrat and Republican alike — spoke at Earth Day events. The Today show devoted 10 hours of airtime to Earth Day. And that mobilization — which was decentralized, mostly achieved through a tiny national office — paved the way for real government action: the Clean Air Act of 1970, the Clean Water Act of 1972, the Endangered Species Act of 1973 and the creation of the Environmental Protection Agency (EPA).

This year’s Earth Day was a little less memorable, and a whole lot less bipartisan. (I can’t imagine a Republican member of Congress giving a speech during Earth Day now unless they were calling for the dismantling of the EPA.) And it comes during a moment of crisis for the environmental movement as it attempts to grapple, so far unsuccessfully, with the existential threat of climate change. Back to Lemann:

Then, 40 years after Earth Day, in the summer of 2010, the environmental movement suffered a humiliating defeat as unexpected as the success of Earth Day had been. The Senate Majority Leader, Harry Reid, announced that he would not bring to a vote a bill meant to address the greatest environmental problem of our time — global warming. The movement had poured years of effort into the bill, which involved a complicated system for limiting carbon emissions. Now it was dead, and there has been no significant environmental legislation since. Indeed, one could argue that there has been no major environmental legislation since 1990, when President George H.W. Bush signed a bill aimed at reducing acid rain. Today’s environmental movement is vastly bigger, richer and better connected than it was in 1970. It’s also vastly less successful. What went wrong?

Forty-three years after the first Earth Day, are Lemann and other critics of the modern environmental movement right? Have greens lost their way — and if so, why?

There’s no getting around the fact that environmentalists have failed to push through a legislative solution to climate change. Cap and trade, even under a Democratic Congress and President, failed in 2010. The international climate regime under the U.N. seems to get closer to collapse every year, and even in much greener Europe, carbon markets simply aren’t working. And environmentalism as a concept doesn’t seem to resonate with Americans as it once did. A new YouGov/HuffPost poll found that Americans are less concerned about the environment now than they were on the first Earth Day. While isolated issues like fracking and the Keystone pipeline resonate strongly with some Americans, especially those who are directly affected — witness the mobbed hearing on the proposed Keystone XL pipeline last week and the stream of antifracking protests — there’s nothing close to the sheer number of Americans who were motivated to take part in the first Earth Day.

What’s changed? You can blame the specific failure of cap-and-trade legislation in part on the mechanics of the U.S. Senate — the bill passed the House, barely — where rural conservative states get outsize representation and where legislation now needs to get 60 votes to pass. (Though of course health care reform still managed to pass despite those same obstacles.) The growing political polarization that has made environmentalism almost solely a Democratic cause can’t be blamed only on greens. But I think the biggest reason is that environmentalism has been a victim of its own success. The environment — everyone’s environment — really was a mess in 1970. Urban rivers were on fire, smog choked the Los Angeles basin, toxic waste affected towns like Love Canal and shorelines were marred by industrial runoff. See this Slateroundup of once polluted or threatened sites in America that have been saved by the environmental movement over the past four decades. Things used to be very, very bad.

And now? The air and water in most of America is much cleaner than it was during the first Earth Day. We have an Environmental Protection Agency to, well, protect the environment, even if it can’t always do the job. The most immediate threats have retreated, and as Michael Kazin points out in the New Republic, that fact alone has hurt environmentalism as an active and broad-based political cause:

Not much has changed since then. However, the most salient reason for the waning of the greens may be rather simple: American voters do not view climate change, unlike issues on which environmentalists won in the past, as an immediate threat to either their health or their wealth. Hurricanes may be stronger, summers hotter and droughts longer than ever. But unless you’re a climate scientist or follow their research closely, it’s difficult to know for sure whether these phenomena signal the beginning of a historic calamity or are merely events on a cyclical pattern. At any rate, supermarkets offer an ever increasing variety of foods at fairly stable prices, while Mardi Gras was celebrated on schedule in New Orleans not long after Katrina blew through. Most coverage of climate change traffics heavily in words like could and potentially. It’s hard to build a world-saving movement on that.

That rings true to me. Environmentalists still have success when the issues they take on are direct and local — see the furor over fracking, or the growth of organic food and BPA-free materials. But no matter what the scientific papers and headlines say, climate change still feels distant to most Americans — important, but still distant. One-off events like Superstorm Sandy can and do move the needle — but not enough, yet, to make climate change a front-and-center issue for most Americans. We’re pretty good at paying attention to the here and now, and really bad at planning for the future — half of us aren’t even saving for our own retirement. Building a nationwide coalition around a problem of the future is like trying to grasp fog.

So maybe we should stop comparisons with the first Earth Day. We may never see 20 million Americans demonstrate over the environment — unless, I suppose, things get much, much worse. And there’s great progress that has been made outside traditional movement politics — look at the way businesses large and small have embraced sustainability in a manner that would have been unimaginable some 40 years ago. But it’s going to take more than that, and it will take more than just greens. Climate change is too big — and too important — to be left to the environmentalists alone.